Above: Image © Juanmonino, iStockphoto

Imagine this: You and your identical twin sibling are, well, identical. You not only look alike, but you share your clothes, your room—and, of course, the same genetics! There is only one big difference. Your twin sister developed asthma. She has used an inhaler since she was little. However, you’ve never had any kind of breathing problems at all. How is this possible?

Well, there is one other not-so-little difference between you and your sister: you were born first. You were pushed out by your mom the natural way: a vaginal delivery. Due to complications, your sister was delivered by a Cesarean section, or C-section. This is a surgery where doctors cut open the abdominal wall and uterus to remove the baby.

In the end, both you and your twin came out safely. Your mom recovered well. However, your sister missed out on the natural process of passing through the vagina. This can have long-term consequences on health, including on the development of allergies and asthma.

Did you know? Babies are delivered by C-section when a vaginal delivery would be too risky. For example, the baby might be positioned awkwardly in the uterus so that it would come out upside down!

Good bacteria

Why does being delivered vaginally affect your health? Passing through the vaginal canal is important for the development of your microbiome—the trillions of bacteria that live on and in your body. Of course, there are bad kinds of bacteria floating around in the environment. These bacteria can make you sick.

However, there are many good kinds of bacteria that live in your lungs, intestines, and many other organs of your body. These bacteria actually keep you healthy. The vagina is filled with these good bacteria. They attach themselves to the newborn baby as it passes through.

This important step ensures babies acquire these healthy bacteria from their mothers’ bodies. Otherwise, babies miss out on these bacteria completely. Instead, babies born by C-section are colonized by the bacteria on the skin of their doctors and parents.

Not surprisingly, birth by C-section completely changes the bacterial make-up of a child’s body. When scientists sample the bacteria from babies’ saliva and stool a few weeks after birth, they see a difference. Vaginally-delivered babies have bacteria that resemble the healthy bacterial population found in the saliva, stool, and vagina of their mothers. Meanwhile, C-section babies have large amounts of bacterial types normally only found on the skin.

Did you know? The “good” bacteria that live inside the vagina during pregnancy act like the baby’s own tiny army! They protect the growing fetus by fending off “bad” bacteria and viruses.

Long-term effects

The effects of a non-vaginal birth are long-lasting. When bacteria is sampled seven years later, children born by C-section still have very different microbiomes. So naturally, scientists started wondering, “How do C-section births affect these children’s long-term health?” And they looked under a microscope for answers.

The microbiome plays an important role in the development of a child’s immune system. Healthy bacteria help the body develop defense mechanisms to recognize and fight off invaders. Examples of invaders include bad bacteria, viruses, and environmental allergens.

The wrong microbiome means that the immune system won’t develop normally. This can lead to conditions like eczema, allergies, and asthma. C-section babies miss out on important immune system development. This makes them more likely to develop these conditions.

Researchers have identified which types of immune-supporting bacteria are present in vaginally-delivered babies and absent in C-section babies. For example, C-section babies have abnormally low levels of a bacterium called Bifidobacteria. It is one of those good vaginal bacteria that normally get picked up during childbirth. Levels of Bifidobacteria are also very low in children with allergies and asthma. So it could help explain why your sister has asthma and you don’t.

Did you know? Your microbiome affects more than just your risk of allergies and asthma. Healthy bacteria may lower your risk of obesity, organ failure, and even cancer.

Helping C-section babies develop a healthy microbiome

At this point, you’re probably convinced that C-section births aren’t a good thing. However, vaginal delivery can be risky in some situations. In these cases, C-sections are necessary to safely deliver the baby. So how can C-section babies develop healthy microbiomes rich in good bacteria?

A group of doctors is trying to answer that question. In a recent study, they gave C-section babies a healthy dose of their moms’ vaginal bacteria. They incubated a piece of gauze inside the mother’s vagina. Then, they wiped the gauze all over the baby’s body as soon as it was delivered. The doctors hoped that this step would imitate passing through the vagina naturally.

A month later, the doctors sampled the babies’ microbiomes. These babies had bacterial profiles that looked more like those of vaginally-delivered babies than of C-section babies. Success! The next step will be to follow up with these babies. This research will show if this “bacterial transfer” has positive effects on their long-term health.

With studies like these, scientists continue to better understand how the microbiome affects the risk of disease. They also find possible ways to control the development of the microbiomes to improve health. Hopefully someday, no matter how they are delivered, twin babies will stay just as they should be: identical!

Learn More!

About the microbiome and vaginal bacteria:

Explore the Human Microbiome [Interactive] (2012)
C. Gorman, Scientific American

How bacteria in the vagina change during pregnancy (2012)
S.E. Gould, Scientific American

About scientific studies on birth and the microbiome:

Partial restoration of the microbiota of cesarean born infants via vaginal microbial transfer (2016)
M.G. Dominguez-bello et al., Nature Medicine 22

Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns (2010)
M.G. Dominguez-bello et al., Proceedings of the National Academy of Science USA 107

Mode of delivery affects the bacterial community of the newborn gut (2010)
G. Biasucci et al., Early Human Development 86
Registration or subscription required to view full text.

Factors influencing the composition of the intestinal microbiota in early infancy (2006)
J. Penders et al., Pediatrics 118
Registration or subscription required to view full text.

The influence of the mode of delivery on circulating cytokine concentrations in the perinatal period (2005)
A. Malamitsi-Puchner et al., Early Human Development 81
Registration or subscription required to view full text.

Influence of mode of delivery on gut microbiota composition in seven year old children (2004)
S. Salminen, G.R. Gibson, A.L. McCartney & E. Isolauri, Gut 53

Mode of delivery and development of atopic disease during first 2 years of life (2004)
K. Negel et al., Pediatric Allergy and Immunology 15
Registration or subscription required to view full text.

Gut flora in health and disease (2003)
F. Guarner & J.R. Malagelada, Lancet 361

Allergy development and the intestinal microflora during the first year of life (2001)
B. Bjorksten, E. Sepp, K. Julge, T. Voor & M. Mikelsaar, Journal of Allergy and Clinical Immunology, 108
Registration or subscription required to view full text.

The intestinal microflora during the first weeks of life (1997)
E. Bezirtzoglou, Anaerobe 3

Sophie Hamr

Sophie My name is Sophie Hamr and I am currently a Master’s student at the University of Toronto studying Human Physiology. Before my Master’s I attended high school in Toronto, Ontario and then did my Undergraduate degree at Dalhousie University in Halifax, majoring in Biology. My studies focus on the hormonal control of body weight and blood glucose in the context of obesity and diabetes, but I am interested in a wide range of scientific topics and especially in scientific communication and education! I hope, through CurioCity, to inspire high school students to get as excited about the world of science as I am.


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